In this study precursors of cortical function and temperament are compared in infants varying in gestational and medical status at birth. The infants to be studied will include healthy as well as previously sick prematures at their expected date of delivery, healthy full-term neonates and postmature neonates. Cortical function will be evaluated by measures of habituation, dishabituation and transfer of learning in response to tactile, auditory and visual repeated stimulation. Temperament will be assessed by measures of states of consciousness, the range and quality of activity while the babies are free of apparent discomfort and by the persistence of spontaneous and elicited crying in the face of experimentally designed attempts to quiet the infants. The results are expected to identify factors which place children at greater than average risk for later intellective and behavioral dysfunction. The results will also provide information about the importance of maturation and medical integrity for the function of different sensory modalities and the organization of behavior.